function newCoor= expandPoint(nearCoor,randCoor,step)
deltaX=randCoor(1)-nearCoor(1);
deltaY=randCoor(2)-nearCoor(2);
deltaZ=randCoor(3)-nearCoor(3);

r=sqrt(deltaX^2+deltaY^2+deltaZ^2);
fai=atan2(deltaY,deltaX);
theta=acos(deltaZ/r);

x=step*sin(theta)*cos(fai);
y=step*sin(theta)*sin(fai);
z=step*cos(theta);
%转化到全局坐标系下
newCoor=[x+nearCoor(1),y+nearCoor(2),z+nearCoor(3)];

end

